Mild Traumatic Brain Injury (mTBI) is a high prevalence injury, caused by the displacement and deformation of the brain in the skull during head/body impacts. Athletes in contact sports at all levels are a high-risk population. It is vitaly important to identify athletes receiving potentially concussive blows on the field in order to prevent further injury and long-term neurological damage. For this purpose, a lot of research has been devoted to on- field monitoring of head accelerations (HACC) following the hypothesis that a high HACC is associated with a higher risk of concussion. So far, it appears that the link between HACC and clinical outcome of mTBI is elusive, because it is not clear how HACC recorded on-field translates to brain displacement and deformation. There is no method that can directly assess brain responses to body/head impacts in live human beings engaged in high-risk activities at this moment. It is recognized that other organs in the head may undergo similar displacement and deformation as the brain during impacts and thus may serve as a surrogate for inferring brain responses. One of these organs is the eye. It has been demonstrated that the eye and the surrounding tissue (the eye mass) undergo a passive (not neurally controlled) mechanical displacement and deformation in the eye socket in a short time window immediately after a HACC. It is thus hypothesized that a direct assessment of the passive eye response (PER) to HACC can be used to better infer brain response to body/head impact, and consequently, can offer a better chance to predict mTBI than HACC itself. Three specific aims will be pursued to test the hypothesis above. (1) Develop a tethered eye sensor that is made of an array of strain gauges packed in a silicone hydrogel wafer and that can be inserted in the inferior cul-de-sac of a human eye. The eye sensor measures dynamic strains at several locations and thus provides real time assessment of eye mass response to impact. It will be tested and refined using an anatomic head model. (2) Record PER induced by daily activities that are known to produce mild, non-concussive HACC. Twenty young, normal human participants will be asked to perform tasks such as sitting into a chair, standing up, walking, running on a treadmill, jumping and moving the eyes while the PER is monitored with the eye sensor. (3) Brain displacement and deformation caused by mild, non-concussive linear and angular HACC will be imaged using tagged MRI in 5 young normal human participants while the HACC and PER are monitored. These experiments will quantify the link between HACC, PER and brain responses, and will lay the foundation for further development of a wireless eye sensor for athletes to wear during games and to identify those who may have received concussive blows.